BDNF and major depressive disorder: An experiment consisting in blocking the behavioral effect of M-5MPEP by a TrkB antagonist, which was not done because of a lack of approval of the ethics committee due to failure to meet the requirement of the 3R principles, would undoubtedly help to finally verify the hypothesis about the dependence of the antidepressant-like effect of M-5MPEP on the activation of the BDNF-TrkB signaling in the CUMS model of depression.